This application claims the priority benefit of Taiwan application serial no. 090100156, filed Jan. 3, 2001, the full disclosure of which is incorporated herein by reference.
1. Field of Invention
The present invention relates to a synthetic method of molecular sieves containing transition metals. More particularly, the present invention relates to a synthetic method of a mesoporous molecular sieve containing Cu and Al in its framework.
The present invention also relates to a method of oxidizing trimethylphenol (TMP) to trimethylbenzoquinone (TMBQ) by using molecular sieves, which comprise the molecular sieve containing Cu and Al in its framework, as catalysts.
2. Description of Related Art
Recently, the global market of Vitamin E has dramatically increased. The main markets are in medical ingredients and nutrition foods. Since the starting material, i.e. 2,3,6-trimethyl-1,4-hydroquinone (TMHQ), is not easily obtained in bulk, the price of Vitamin E is quite high. Therefore, researchers have widely studied how to efficiently manufacture TMHQ at a lower cost.
In the past two decades, many chemical processes have been developed to manufacture TMHQ by using TMP as the starting material. Sumitomo Chemical Company uses chlorine gas to chlorinate TMP, then nitric acid is used to oxidize TMP to TMHQ (U.S. Pat. No. 3,932,475). The advantage of this process is that the price of TMP is quite cheap, but one problem is that it produces a lot of pollutants. More than 50 kg of pollutive effluent is produced for every kilogram of TMHQ. [C. Mercier and P. Chabardes, in M. G. Scaros and M. Prunier (Eds.), Catalysis of Organic Reactions, Marcel Decker, New York, 1994, pp. 213-221 ].
TMP is oxidized to TMBQ, and then TMBQ is hydrogenated to TMHQ by other patents. Catalysts, which can be used in the oxidation step, include MnO2 and saturated organic acids (U.S. Pat. No. 3,927,045), inorganic or organic acids of TI (III) (U.S. Pat. No. 3,910,967), chelating complexes of Co (U.S. Pat. No. 4,250,335), complexes of Fe or Mn (U.S. Pat. No. 5,712,416), cupric oxide or cuprous oxide (U.S. Pat. No. 4,491,545), and aqueous solutions (U.S. Pat. No. 4,828,762) or saturated alcohol solutions (U.S. Pat. No. 5,041,572) of cuprous halide/alkaline metal halide. Generally used catalysts in the hydrogenation step include platinum or palladium supported on zeolites or aluminum oxide, and hydrogen gas is used to hydrogenate TMBQ to TMHQ (U.S. Pat. No. 4,491,545 and U.S. Pat. No. 4,828,762).
Some papers about oxidizing TMP to TMBQ are published, such as Ito et al. (S. Ito, K. Aihara, M. Matsumoto, Tetrahedron Lett., 1983, 24, 5249), have used many kinds of metal oxides and metal salts as catalysts, acetic acid and 30% hydrogen peroxide solution are respectively used as a solvent and an oxidant. They found that the best reaction result was obtained when RuCl3 was used as the catalyst. The yield of TMBQ was up to 90%. Since RuCl3 is readily soluble in the reaction solution, RuCl3 is hardly separated from the solution to be reusable. Furthermore, the cost of RuCl3 is quite high, and thus this method is not economic.
Japanese Shimizu et al. (M. Shimizu, H. Orita, T. Hagakawa, K. Takehira, Tetrahedron Lett., 1989, 30, 471) and Russian Kholdeeva et al. (O. A. Kholdeeva, A. V. Golovin, R. I. Maksimovskaya, I. V. Kozhenikov, J. Mol. Catal., 1992, 75, 235) respectively use hetero-polyacids and acetic acid to be the catalyst and the solvent. When 60% wt. H2O2 is used as the oxidant, the yield of TMBQ is the highest (about 80%). However, the consumption of H2O2 is very large, and the hetero-polyacids are too readily soluble in water to be isolated from the reaction solution to be reused again.
Dutchman Jansen et al. used hetero-polyacids adsorbed on active carbons as catalyst (J. J. Jansen, H. M. van Neldhuizen, H. van Bekkum, J. Mol. Catal. A, 1996, 107, 241), therefore he hoped to increase the easiness of separating the catalyst from the reaction solution. However, washout of hetero-polyacids adsorbed on active carbons is still occurring, thus the practicability is not high.
The turn over number (TON) of catalysts used in the above references is at most about 4-10. Most oxidation catalysts mentioned above are soluble in organic solvents or water; therefore solvents are needed for recycling these oxidation catalysts to extract them from the reaction mixtures. This extraction procedure makes the whole reaction process more complicated and it still has a large space to improve.
The widest used molecular sieve is the zeolite, of which pore size is in the microporous range, i.e. about 0.5-1 nm. Therefore, it""s only application was in catalyzing chemical reactions of small molecules. However, the development of mesoporous molecular sieves, of which pore size is about 2-10 nm, has made them applicable in catalyzing chemical reaction of larger molecules, especially in cracking heavy oil and production of drugs and fine chemicals. When transition metal is added in the molecular sieve, the reaction types that can be catalyzed by the molecular sieve have expanded from acid catalyzed reaction to redox reaction.
In the last ten years, molecular sieves containing transition metal have been popular to be used in synthesis of TMBQ in order to resolve the problem of recovering catalysts from homogeneous reaction systems. For example, liquid reaction system using zeolites containing Ti or V as catalysts and aqueous solution of H2O2 as oxidant can effectively oxidize phenol to hydroquinone and catechol (J. S. Reddy, S. Sivasanker and P. Ratnasamy, J. Mol. Catal., 1992, 71, 373 and A. V. Ramaswany, S. Sivasanker and P. Ratnasamy, Micro. Mater., 1994, 2 , 451). Molecular sieves containing copper ions are used in decomposing NO, and those molecular sieves containing Cu2+ are prepared by ion-exchange between cations of molecular sieves and Cu2+.
The invention provides a method of oxidizing trimethylphenol (TMP) to trimethylbenzoquinone (TMBQ).
In this method, TMP, a molecular sieve containing a transition metal in its framework, an oxidant and a solvent are mixed to form a reaction system, and the reaction system reacts at a suitable temperature to obtain TMBQ. The concentration of the TMP is about 5-60% wt. The reaction temperature is about room temperature to about 150xc2x0 C., the preferred reaction temperature is about 40-80xc2x0 C., and the more preferred temperature is about 50-60xc2x0 C.
The molecular sieve that can be used in this invention comprises a zeolite, a mesoporous molecular sieve of hexagonal or cubic lattice structure, and an aluminophosphate molecular sieve. The transition metal described above can be Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ru and W, and the amount of the transitioin metal is about 0.1-10% wt. of the molecular sieve.
The zeolite described above can be ZSM-5, ZSM-11, Zeolite-Y, Zeolite-X, Zeolite-A or xcex2-zeolite. The mesoporous molecular sieve described above comprises MCM-41 and MCM-48, and the preferred ones are MCM-41 containing V or Cu/Al. The aluminophosphate molecular sieve described above comprises AIPO4-5, AIPO4-8, AIPO4-11, AIPO4-31, SAPO-37 and VPI-5, and the preferred ones are AIPO4-5 containing Ti, Co or Cu.
The oxidant""s concentration described above is about 5-60% wt., and it comprises H2O2 or ROOH such as t-BuOOH. If oxygen gas is used as oxidant, the O2 flows into the reaction system at a flow rate of 1-20 mL/min.
The solvent""s concentration described above is about 5-60% wt., and it can be nitrites such as CH3CN; alcohols such as methanol, ethanol, propanol and butanol; aldehydes such as CH3CHO and PhCHO; and carboxylic acids such as acetic acid.
This invention also provides a method of forming a mesoporous molecular sieve containing Cu and Al in the framework.
In this method, a Si-containing compound, a Cu-containing compound, a Al-containing compound, a template reagent and a solvent are mixed together to obtain a mixing solution. In the mixture solution, the Al/Si molar ratio is between about 0-0.2, the Cu/Si molar ratio is between about 0-0.1, and the template reagent/Si molar ratio is between about 0.1-2.
The Si-containing compound can be an inorganic silicate such as water glass (sodium silicate), or an organic Si-containing compound such as tetraethoxysilicate (TEOS). The Cu-containing compound can be an inorganic copper salt such as Cu(NO3)2. The Al-containing compound can be an inorganic aluminate such as sodium aluminate, or an organic Al-containing compound such as triethoxyaluminate or tripropoxyaluminate.
The template reagent can be a tetraethyl ammonium salt, a tetrapropyl ammonium salt, a long-chain-alkyl-trimethyl ammonium salt, a copolymer or combinations thereof. The carbon number of the long-chain-alkyl-trimethyl ammonium salt is 12-20. The solvent can be water, methanol, ethanol, propanol, butanol or combinations thereof. The only requirement for mixing various solvents is that these solvents can form a single-phase system.
The pH of the mixture solution is adjusted to about 9-11 when the mixing solution""s pH is larger than 11, or the mixture solution""s pH is adjusted to about 0.1-3 when the solution""s pH is 3-9. The adusting pH step can be accomplished by adding acids such as common used HCl, HNO3 or H2SO4.
The mixture solution undergoes a hydrothermal reaction under a temperature of about 80-200xc2x0 C. for about 1-10 days to form the mesoporous molecular sieves. Precipitate is separated from the products of the hydrothermal reaction, and then it is washed and dried. The precipitate is calcined at a temperature of about 500-800xc2x0 C. to remove the template reagent in the mesoporous molecular sieve""s pores.